[MarkS57]

Curious, for the 76 - 77 350's with the large valve 6x heads. Are these engines limited in valve lift due to the large valves or are there chamfers in the cylinders. I suspect there are on the intake side. Follow up, as the exhaust valve on a 62 head is 1.77" and the intake valves on a small valve head are larger than that, is there any lift issue using 1.77's on the later 350?

[steve25]

Well first let’s talk about how much HP you’re looking to have under control of your right foot.

I as because there’s a pretty solid rule you can go by.
It states that for every 100 hp you want to make that you need to run .100” of intake valve lift.

Because I know someone will likely try to discredit that and since we are taking about a 350s 3.88” bore let’s say you need to run .115” lift for every 100 hp you want to make.

[steve25]

Mark here’s what you’re dealing with.

Note that in my photos my flow bench adapter plate I made is for a .030” 350, or a 3.91” bore.

The shallow side of a 6X head be it a dash 4 or dash 8 is .240” deep.
The head in my photos is a dash 4 just to be clear.
So this is what I found.
this means that with
No head gasket and
Zero deck
You can only run .470” lift when using the 2.11” valve before the valve hitting the cylinder wall.

The shallow side of a high comp 670 head head for example is about .200” deep.

My second photo is a 1.96” valve in the 6X head and there’s no issue with it hitting the cylinder wall.

It would be nice to have a chamfer at the top of the bore with a 1.96” valve , but in my opinion a 2.11” valve demands it .

Keep in mind that Pontiac used chamfers even in the bore of many 455 motors.

[MarkS57]

Originally Posted by steve25

Mark here’s what you’re dealing with.

Note that in my photos my flow bench adapter plate I made is for a .030” 350, or a 3.91” bore.

The shallow side of a 6X head be it a dash 4 or dash 8 is .240” deep.
The head in my photos is a dash 4 just to be clear.
So this is what I found.
this means that with
No head gasket and
Zero deck
You can only run .470” lift when using the 2.11” valve before the valve hitting the cylinder wall.

The shallow side of a high comp 670 head head for example is about .200” deep.

My second photo is a 1.96” valve in the 6X head and there’s no issue with it hitting the cylinder wall.

It would be nice to have a chamfer at the top of the bore with a 1.96” valve , but in my opinion a 2.11” valve demands it .

Keep in mind that Pontiac used chamfers even in the bore of many 455 motors.

Hi Steve, I'm looking at a 77 350 I want to wake up. I have a nice set of 62's that can bolt on tomorrow. So, beyond an 068 which I know will work, I'm considering a 2801 that gets close to .470.

[srmmmm]

Originally Posted by steve25

Mark here’s what you’re dealing with.

Note that in my photos my flow bench adapter plate I made is for a .030” 350, or a 3.91” bore.

The shallow side of a 6X head be it a dash 4 or dash 8 is .240” deep.
The head in my photos is a dash 4 just to be clear.
So this is what I found.
this means that with
No head gasket and
Zero deck
You can only run .470” lift when using the 2.11” valve before the valve hitting the cylinder wall.

The shallow side of a high comp 670 head head for example is about .200” deep.

My second photo is a 1.96” valve in the 6X head and there’s no issue with it hitting the cylinder wall.

It would be nice to have a chamfer at the top of the bore with a 1.96” valve , but in my opinion a 2.11” valve demands it .

Keep in mind that Pontiac used chamfers even in the bore of many 455 motors.

My 1970 350 block is bored .060 over with .003 milled off the deck. The 6X-4 heads were milled .005 and Butler performance head gaskets used with a crush thickness of .045
Pistons are Ross flat top set even with deck height, Cam is Comp XE276HR with .502/.510 lift and 224/230 duration @.050 with 1.5 rockers.
442 Lb Ft @ 4300 and 453 HP @ 5600

[steve25]

Thanks much for posting the above info, but if he’s at .030” and not .060” then your being .060” over and the fact that your chamber is .03 something deeper then his ( in his 62 castings ) might be the the only thing that’s keeping you with your .060” over 350 out of trouble.


The only way I can come up with for Mark with an assembled head to prove out his 62 heads would work is this.

Get one of these KD tools spring compressor bars.

Sit the head on with no gasket.

Put few head bolts in sung.

Then slowly compress the spring and measure how far you can go.

If your ok at .470” lift then the head gasket will give you the needed hot running clearance.

Be sure to have the piston up close enough so that when compressing if the keepers let go you don’t drop the valve out all the way.



In post number 5 would I be correct in assuming by your posted HP levels that your 6X heads where ported?

[srmmmm]

Originally Posted by steve25

Thanks much for posting the above info, but if he’s at .030” and not .060” then your being .060” over and the fact that your chamber is .03 something deeper then his ( in his 62 castings ) might be the the only thing that’s keeping you with your .060” over 350 out of trouble.

In post number 5 would I be correct in assuming by your posted HP levels that your 6X heads where ported?

Engine builder (Len Williams) told me maximum lift measured out to .520 on my engine config.
The heads were not ported, but the Torker-I intake was port matched and the quadrajet is from a Buick GS455 Stage-I. The dyno headers were Hooker, 1-3/4" X 30"

[MarkS57]

Originally Posted by steve25

<SNIP>

The only way I can come up with for Mark with an assembled head to prove out his 62 heads would work is this.

Get one of these KD tools spring compressor bars.

Sit the head on with no gasket.

Put few head bolts in sung.

Then slowly compress the spring and measure how far you can go.

If your ok at .470” lift then the head gasket will give you the needed hot running clearance.

Be sure to have the piston up close enough so that when compressing if the keepers let go you don’t drop the valve out all the way.

<SNIP>

Thanks Steve, good idea. I have a nice spring compressor to use.

[steve25]

That’s good mark. I just hope you can move the valve enough to reach the limit you need to confirm.

Since you have a valve compressor I might take that spring off and then reassemble it with just the outer spring and then the lesser force needed to open the valve should allow you to open it as far as necessary without the keepers popping out on you.

[Squidward]

When I built my 72 350, I put the heads on with a used gasket, and checked max lift with low tension checking springs. Block had 2 chamfers each cylinder, at 40 over. I measured max lift of .509 with my big valve #12's before the valve contacted the bore. As a result, I made sure to keep my lift reasonable, so I went with the Lunati Voodoo 702 (219/227 @50, .468/.489 with 1.5 rockers). Checking with NO gasket would give even greater margin, and would build in a safety factor by the gasket thickness.

As mentioned, the safest plan is to measure, for sure. I checked a set of 061 heads I have, and the valve to deck clearance was definitely smaller. Rebuilds, milling, decking, etc can all stack up.

Thinking an 068 would be easily doable. And at .444/.466, the 2801 would likely be a fun cam in a 350 with the right converter and gears.

[Squidward]

Exhaust valve lift will be your constraint. Later 2.11/1.66 heads will likely give you more lift with the smaller exhaust valve.

Steve has probably forgot more than I will ever learn, so not looking to dispute. I just never saw an issue with the intake valve clearance, but the exhaust was the constraint in my setup.

The original heads on this motor were 72 7H1 heads, which were 1.96/1.77 valves. Cam lift was small in that application, tho. Weird.

Glad there are more "tree-fiddy" motors getting some love!

[242177P]

Nice seeing the 2.11 clear that small bore. As Squidward says,
deck clearance will change depending on casting used.

Now here's the $60,000 dollar question: at what point do you
sacrifice valve lift for compression? There's like 20cc worth of
difference between the late 6X-4s and early 17s (IIRC).

And if it's just some bowl blending, you could add a big valve
to a '69 47. There's enough variables to make one's head spin,
but it's all so very intriguing.

[srmmmm]

Originally Posted by 242177P

Nice seeing the 2.11 clear that small bore. As Squidward says,
deck clearance will change depending on casting used.

Now here's the $60,000 dollar question: at what point do you
sacrifice valve lift for compression? There's like 20cc worth of
difference between the late 6X-4s and early 17s (IIRC).

And if it's just some bowl blending, you could add a big valve
to a '69 47. There's enough variables to make one's head spin,
but it's all so very intriguing.

Going to a 4.25" stroke, the 6X-4 heads gave me a comfortable CR of about 9.3 to 1. I've had no issues running 92-93 octane in it as a result.

[Squidward]

Originally Posted by 242177P

And if it's just some bowl blending, you could add a big valve
to a '69 47. There's enough variables to make one's head spin,
but it's all so very intriguing.

That's what I had done to the 47's on the 400 in my Lemans - big valves. Paul Carter did those heads, and said his previous testing showed an increase in flow numbers.

[steve25]

I don’t think his late 70s 350 block has the valve chamfers to provide whatever amout of added clearance that it does.

Like I posted, I hope he can get away with .470” lift without a head gasket in place.

[MarkS57]

Thanks to all that have replied. I found a picture of a 75 block in a search here. It shows exhaust valve chamfers, no intake chamfers. (thanks go to Jay S for the pic). The casting # of that 75 block should be the same as the 77 (488986). I guess they could have left out the exhaust chamfer in the block machining in 77 but seems unlikely? In any event, there's also the lack of valve reliefs in the stock pistons and the shallower chambers. In the end, doing as Steve suggests- plopping the 62's on the block w/o a head gasket & measuring will tell me the story.

[steve25]

Yup, the 73 thru 77 350 pistons are listed as being flat with no valve notches. :-(

Looks like your heading for the 068 cam for the 62 heads, but check what you have none the less.

[MarkS57]

Originally Posted by steve25

Yup, the 73 thru 77 350 pistons are listed as being flat with no valve notches. :-(

Looks like your heading for the 068 cam for the 62 heads, but check what you have none the less.

I even have an 068 so if that's it, that's ok. Well, there's the 744, Wonder if that one's ever been done.

[steve25]

Under 10 to 1 and the 744 Cam will not be make for happy times in a 350.